In a digital communication system, a receiver receives a radio-frequency (RF) modulated signal from a transmitter. The receiver downconverts the received signal from RF to baseband, digitizes the baseband signal to generate samples, and digitally processes the samples to recover data sent by the transmitter. The receiver may use one or more downconversion mixers to downconvert the received signal from RF to baseband.
An ideal mixer simply translates an input signal from one frequency to another without distortion. In integrated circuits, however, the mixer's performance may deviate from the ideal case due to mismatch between the transistors caused by, e.g., layout or process variations. Such mismatch may introduce distortion into the output of the mixer, leading to unwanted inter-modulation products. For example, in a mixer for a direct conversion receiver, second-order inter-modulation (IM2) products in particular may especially degrade the signal-to-noise ratio (SNR) at baseband. While symmetrical layout and differential signal processing can help reduce the effects of device mismatch, there may still be residual mismatch due to process limitations.
Disclosed herein are techniques to provide for configurable parameters in a mixer to calibrate and correct for such mismatch, thereby minimizing mixer distortion.